低温SCR脱硝催化剂抗SO2中毒的微观机制

The research and development of low-temperature active selective catalytic reduction (LT-SCR) of NOX with NH3 are of great importance for the promotion of ultra-low emission of NOX in China. However, the SO2 induced catalyst deactivation is still one of the main barriers for its real application. With our recent achievements on the rare earth oxide based LT-SCR catalysts development as background, in this proposal, we plan to approach the effects of catalyst surface structures, including exposed facets, surface atom arrangement, and surface defects, on the adsorption and activation of the molecules involved into the low-temperature SCR process (for example NOX, NH3, O2 and SO2) by both simulation and experimentation. Especially the impact of the interaction between SO2 and catalyst on the de-NOX paths will be systematically investigated, at the same time, the impact of SO2 on the catalyst structure evolution, thermal dynamic and kinetic parameters change will be clarified. Accordingly, the possible reaction paths to suppress the SO2 induced catalyst deactivation will be evaluated and optimized. For catalyst preparation, wet chemical methods such as sol-gel and solvothermal methods will be optimized to control the rare earth oxide based catalysts with expected structures according to simulation. And SEM, TEM, XRD, TGA, IR, TPD, TPR, and TPO techniques will be applied to characterize the structure, acidity, redox ability, and adsorption ability of the prepared catalysts, trying to evaluate simulation approaches and experimental results. Furthermore, in situ HRTEM observation under real SCR reaction conditions performed in a closed gas cell system at atmospheric pressure will be used to investigate the interaction between SO2 and catalysts, to try to further clarify the mechanism of SO2 induced catalyst deactivation and regeneration from the view of catalyst microstructure evolution, and also the reaction between reactant molecules and catalyst will be visualized. We believe that after the implementation of the this project, the mechanisms of LT-SCR and the resistance of SO2 induced catalyst deactivation will be clarified, and a series of rare earth oxide based catalysts with excellent LT-SCR efficiency and strong SO2 resistance will be optimized.

低温NH3-SCR脱硝技术的研发对推进我国NOX的超低排放至关重要，但是催化剂的SO2中毒已经成为阻碍其工业化应用的瓶颈。本项目拟以稀土氧化物为催化剂活性成分，首先从理论模拟入手，设计催化剂的晶面结构、表面原子浓度、表面缺陷等，系统考察催化剂的表面结构与反应物分子的相互作用规律，从原子级别考察反应分子的活化路径及其对低温脱硝历程的作用机理；从反应历程的热力学和动力学参数，获得催化剂抗SO2中毒的可能途径。然后，采用溶胶凝胶、溶剂热等湿化学制备工艺，结合SEM、TEM 、XRD、TGA、IR、TPD、TPR、TPO等分析表征方法，实现稀土氧化物催化剂的表面结构和性能调控，从实验上验证理论模拟的结果。并利用HRTEM的gas cell技术，原位研究在模拟工况下的SO2对催化剂微观结构的作用规律，使相关反应可视化。最终揭示催化剂的抗SO2中毒机理，并制备出抗SO2中毒的低温SCR脱硝催化剂。

低温NH3-SCR脱硝技术对推进我国NOX的超低排放至关重要，项目针对MnOX/CeO2催化剂协同机制和低温抗SO2中毒展开了系统研究。首先从理论模拟实验入手，系统研究了Mn-Ce之间的协同作用本质，发现Mn2+-Ce4+离子之间的电荷化转移是其协同作用的本质 ，以此协同为基础，在低温脱硝过程中在催化剂表面形成了一个Mn-氧化还原循环和一个Ce-氧化还原循环。其中Mn-循环涉及两个Mn3+离子，一个起到路易斯酸的作用，一个起到氧化的作用，达到吸附活化NH3的效果，而Ce-循环涉及到表现氧空位的生成和对O2分子的活化，这样从原子级别揭示了反应分子的活化路径及其对低温脱硝历程的作用机理。第二，把脱硝反应搬进TEM，利用HRTEM的gas cell技术，原位研究在模拟工况下的SO2对催化剂微观结构的作用规律，实现了过程的可视化，并且发现在MnOX/CeO2催化剂上，可以通过表面硫酸盐的沉积-转化-低温分解的动态平衡实现低温抗SO2中毒。第三，系统研究了低温下催化剂上N2O的生成机制，发现NH3的过渡氧化是低温SCR过程中笑气产生的主要途径。第四，与相关企业合作，把所优化的低温SCR催化剂负载在陶瓷过滤器和整体式蜂窝状催化剂载体上，成功进行了工业化示范。在水泥窑上在160-200℃的温度范围内，脱硝效率超过75%。在玻璃窑上，成功实现除尘脱硝一体化，脱硝效率和除尘效率都超过90%。